Method of downlink HARQ operation at an expiry of time alignment timer

ABSTRACT

According to one embodiment, a method of processing data for a Hybrid Automatic Repeat Request (HARQ) operation in a wireless communication system includes: receiving control signaling from a network; receiving data based on the received control signaling; generating a positive response message (ACK) if the received data is successfully decoded or a negative response message (NACK) if the received data is not successfully decoded, wherein the generated ACK or the generated NACK is not transmitted to the network when a timer is expired or not running; and combining the received data with data currently in a buffer after the timer is stopped or expired.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/545,855, filed on Jul. 10, 2012, now U.S. Pat. No. 8,681,704, whichis a continuation of U.S. application Ser. No. 12/863,972, filed on Jul.21, 2010, now U.S. Pat. No. 8,243,657, which is the National Stagefiling under 35 U.S.C. 371 of International Application No.PCT/KR2009/000496, filed on Feb. 2, 2009, which claims the benefit ofearlier filing date and right of priority to Korean Application No.10-2009-0007144, filed on Jan. 29, 2009, and also claims the benefit ofU.S. Provisional Application Ser. No. 61/025,311, filed on Feb. 1, 2008,the contents of which are all incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to a radio (wireless) communication systemproviding a radio communication service and a mobile terminal, and moreparticularly, to a method of downlink HARQ operation of the mobileterminal in an Evolved Universal Mobile Telecommunications System(E-UMTS) or a Long Term Evolution (LTE) system.

BACKGROUND ART

FIG. 1 shows an exemplary network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as a mobile communicationsystem to which a related art and the present invention are applied. TheE-UMTS system is a system that has evolved from the existing UMTSsystem, and its standardization work is currently being performed by the3GPP standards organization. The E-UMTS system can also be referred toas a LTE (Long-Term Evolution) system.

The E-UMTS network can roughly be divided into an E-UTRAN and a CoreNetwork (CN). The E-UTRAN generally comprises a terminal (i.e., UserEquipment (UE)), a base station (i.e., eNode B), an Access Gateway (AG)that is located at an end of the E-UMTS network and connects with one ormore external networks. The AG may be divided into a part for processinguser traffic and a part for handling control traffic. Here, an AG forprocessing new user traffic and an AG for processing control traffic canbe communicated with each other by using a new interface. One eNode Bmay have one or more cells. An interface for transmitting the usertraffic or the control traffic may be used among the eNode Bs. The CNmay comprise an AG, nodes for user registration of other UEs, and thelike. An interface may be used to distinguish the E-UTRAN and the CNfrom each other.

The various layers of the radio interface protocol between the mobileterminal and the network may be divided into a layer 1 (L1), a layer 2(L2) and a layer 3 (L3), based upon the lower three layers of the OpenSystem Interconnection (OST) standard model that is well-known in thefield of communications systems. Among these layers, Layer 1 (L1),namely, the physical layer, provides an information transfer service toan upper layer by using a physical channel, while a Radio ResourceControl (RRC) layer located in the lowermost portion of the Layer 3 (L3)performs the function of controlling radio resources between theterminal and the network. To do so, the RRC layer exchanges RRC messagesbetween the terminal and the network. The RRC layer may be located bybeing distributed in network nodes such as the eNode B, the AG, and thelike, or may be located only in the eNode B or the AG.

FIG. 2 shows exemplary control plane architecture of a radio interfaceprotocol between a terminal and a UTRAN (UMTS Terrestrial Radio AccessNetwork) according to the 3GPP radio access network standard. The radiointerface protocol as shown in FIG. 2 is horizontally comprised of aphysical layer, a data link layer, and a network layer, and verticallycomprised of a user plane for transmitting user data and a control planefor transferring control signaling. The protocol layer in FIG. 2 may bedivided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based upon thelower three layers of the Open System Interconnection (OSI) standardsmodel that is widely known in the field of communication systems.

Hereinafter, particular layers of the radio protocol control plane ofFIG. 2 and of the radio protocol user plane of FIG. 3 will be describedbelow.

The physical layer (Layer 1) uses a physical channel to provide aninformation transfer service to a higher layer. The physical layer isconnected with a medium access control (MAC) layer located thereabovevia a transport channel, and data is transferred between the physicallayer and the MAC layer via the transport channel. Also, betweenrespectively different physical layers, namely, between the respectivephysical layers of the transmitting side (transmitter) and the receivingside (receiver), data is transferred via a physical channel.

The Medium Access Control (MAC) layer of Layer 2 provides services to aradio link control (RLC) layer (which is a higher layer) via a logicalchannel. The RLC layer of Layer 2 supports the transmission of data withreliability. It should be noted that if the RLC functions areimplemented in and performed by the MAC layer, the RLC layer itself maynot need to exist. The PDCP layer of Layer 2 performs a headercompression function that reduces unnecessary control information suchthat data being transmitted by employing Internet Protocol (IP) packets,such as IPv4 or IPv6, can be efficiently sent over a radio interfacethat has a relatively small bandwidth.

The Radio Resource Control (RRC) layer located at the lowermost portionof Layer 3 is only defined in the control plane, and handles the controlof logical channels, transport channels, and physical channels withrespect to the configuration, reconfiguration and release of radiobearers (RB). Here, the RB refers to a service that is provided by Layer2 for data transfer between the mobile terminal and the UTRAN.

As for channels used in downlink transmission for transmitting data fromthe network to the mobile terminal, there is a Broadcast Channel (BCH)used for transmitting system information, and a downlink Shared Channel(SCH) used for transmitting user traffic or control messages. A downlinkmulticast, traffic of broadcast service or control messages may betransmitted via the downlink SCH or via a separate downlink MulticastChannel (MCH). As for channels used in uplink transmission fortransmitting data from the mobile terminal to the network, there is aRandom Access Channel (RACH) used for transmitting an initial controlmessage, and an uplink Shared Channel (SCH) used for transmitting usertraffic or control messages.

As for downlink physical channels for transmitting informationtransferred via the channels used in downlink transmission over a radiointerface between the network and the terminal, there is a PhysicalBroadcast Channel (PBCH) for transmitting BCH information, a PhysicalMulticast Channel (PMCH) for transmitting MCH information, a PhysicalDownlink Shared Channel (PDSCH) for transmitting PCH and a downlink SCHinformation, and a Physical Downlink Control Channel (PDCCH) (also,referred to as ‘DL L1/L2 control channel’) for transmitting controlinformation provided by the first and second layers such as a DL/ULScheduling Grant, and the like. As for uplink physical channels fortransmitting information transferred via the channels used in uplinktransmission over a radio interface between the network and theterminal, there is a Physical Uplink Shared Channel (PUSCH) fortransmitting uplink SCH information, a Physical Random Access Channel(PRACH) for transmitting RACH information, and a Physical Uplink ControlChannel (PUCCH) for transmitting control information provided by thefirst and second layers, such as a HARQ ACK or NACK, a SchedulingRequest (SR), a Channel Quality Indicator (CQI) report, and the like.

In LTE system, a HARQ operation is performed in a MAC (Medium AccessControl) layer for an effective data transmission. The following is adetailed description of the HARQ operation.

FIG. 4 is an exemplary view showing a HARQ operation method for aneffective data transmission. As illustrated in FIG. 4, a base station(or eNB) may transmit downlink scheduling information (referred as ‘DLscheduling information’ hereafter) through a PDCCH (Physical DownlinkControl Channel) in order to provide data to a terminal (UE) during aHARQ operation. The DL scheduling information may include a UEidentifier (UE ID), a UE group identifier (Group ID), an allocated radioresource assignment, a duration of the allocated radio resourceassignment, a transmission parameter (e.g., Modulation method, payloadsize, MIMO related information, etc), HARQ process information, aredundancy version, or a new data indicator (NID), etc.

Here, the DL scheduling information may be transmitted through a controlchannel such as a PDCCH, and the DL scheduling information may be variedwith a channel conditions or circumstances. For example, if a currentchannel condition is better than a channel condition of an initialtransmission, higher bit rate may be used by manipulating a modulationscheme or a payload size. In contrast, if a current channel condition isworst than a channel condition of an initial transmission, lower bitrate may be used.

The terminal checks the DL scheduling information by monitoring a PDCCHin every TTI. Then, the terminal receives data through a PUSCH based onthe DL scheduling information. Once the terminal receives the data, thereceived data is stored in a soft buffer, and then the terminal attemptsto decode the stored data. If the terminal successfully decodes thedata, the terminal transmits an ACK signal to the base station. If theterminal does not successfully decode the data, the terminal transmits aNACK signal to the base station. After that, if the base stationreceives the ACK signal from the terminal, the base station transmits anext data with an assumption that previous data transmission wassuccessfully performed. If the base station receives the NACK signal,the base station retransmits same data with a same transmission formator a different transmission format. After the NACK signal is transmittedto the base station by the terminal, the terminal transmitted the NACKsignal would expect to receive a retransmission of the data. Here, thevalue in the NDI (New Data Indicator) field contained in the PDCCH maybe used for the UE to determine whether the received data is an initialtransmission data or a retransmitted data. More specifically, the NDIfield is 1 bit field that toggles every time a new data is transmittedor received. (0→1→0→1→ . . . ) As such, the value in the NDI for theretransmitted data always has a same value used in an initialtransmission. From this, the UE may know an existence of retransmitteddata by comparing these values.

Description of an uplink timing alignment maintenance in a LTE systemwill be given. In the LTE system that based on an Orthogonal FrequencyDivision Multiplex (OFDM) technology, there is possibility ofinterferences between terminals (UEs) during a communication between UEand base station (eNB). In order to minimize interferences betweenterminals, it is important that the base station must manage or handle atransmission timing of the UE. More particularly, the terminal may existin random area within a cell, and this implies that a data transmissiontime (i.e., traveling time of data from UE to base station) can bevaried based on a location of the terminal. Namely, if the terminal iscamped on edge of the cell, data transmission time of this specificterminal will be much longer than data transmission time of thoseterminals who camped on a center of the cell. In contrast, if theterminal is camped on the center of the cell, data transmission time ofthis specific terminal will be much shorter than data transmission timeof those terminals who camped on the edge of the cell. The base station(eNB) must manage or handle all data or signals, which are transmittedby the terminals within the cell, in order to prevent the interferencesbetween the terminals. Namely, the base station must adjust or manage atransmission timing of the terminals upon each terminal's condition, andsuch adjustment can be called as the timing alignment maintenance. Oneof the methods for maintaining the timing alignment is a random accessprocedure. Namely, during the random access procedure, the base stationreceives a random access preamble transmitted from the terminal, and thebase station can calculate a time alignment (Sync) value using thereceived random access preamble, where the time alignment value is toadjust (i.e., faster or slower) a data transmission timing of theterminal. The calculated time alignment value can be notified to theterminal by a random access response, and the terminal can update thedata transmission timing based on the calculated time alignment value.In other method, the base station may receive a sounding referencesymbol (SRS) transmitted from the terminal periodically or randomly, thebase station may calculate the time alignment (Sync) value based on theSRS, and the terminal may update the data transmission timing accordingto the calculated time alignment value.

As explained above, the base station (eNB) may measure a transmissiontiming of the terminal though a random access preamble or SRS, and maynotify an adjustable timing value to the terminal. Here, the timealignment (Sync) value (i.e., the adjustable timing value) can be calledas a time advance command (referred as ‘TAC’ hereafter). The TAC may beprocess in a MAC (Medium Access control) layer. Since the terminal doesnot camps on a fixed location, the transmission timing is frequentlychanged based on a terminal's moving location and/or a terminal's movingvelocity. Concerning with this, if the terminal receives the timeadvance command (TAC) from the base station, the terminal expect thatthe time advance command is only valid for certain time duration. A timealignment timer (TAT) is used for indicating or representing the certaintime duration. As such, the time alignment timer (TAT) is started whenthe terminal receives the TAC (time advance command) from the basestation. The TAT value is transmitted to the terminal (UE) through a RRC(Radio Resource Control) signal such as system information (SI) or aradio bearer reconfiguration. Also, if the terminal receives a new TACfrom the base station during an operation of the TAT, the TAT isrestarted. Further, the terminal does not transmit any other uplink dataor control signal (e.g., data on physical uplink shared channel (PUSCH),control signal on Physical uplink control channel (PUCCH)) except forthe random access preamble when the TAT is expired or not running.

In general, a MAC layer of the terminal and base station handles a timealignment (synchronize) management. Namely, The TAC is generated in theMAC layer of the base station, and the MAC layer of the terminalreceives the TAC through a MAC message from the base station. However,because the TAC is received by the MAC message, a transmission of theTAC is not fully guaranteed. For example, the base station transmits theMAC message including the TAC in a HARQ process, and the terminalattempts to receive the data. The terminal transmits a NACK signal tothe base station if the terminal fails to decode the data. However, ifsuch NACK signal is mistakenly treated as an ACK signal by the basestation, a TAT of the base station is restarted whereas a TAT of theterminal is not restarted. Thusly, a failed synchronization can behappened between the terminal and base station. In this case, if thereis data to be transmitted to the terminal from the base station, thebase station transmits a PDCCH and a PUSCH to the terminal. Usually, thePDCCH includes a control signal for a data transmission and the PUSCHincludes an actual data. However, the uplink transmission is prohibitedbecause the terminal is not time-aligned with the base station, therebytransmitting an ACK or NACK signal to the base station. However, thiscauses a great drawback of wasting unnecessary radio resource(s).

DISCLOSURE OF INVENTION Technical Solution

Therefore, an object of the present invention is to provide a method ofprocessing data for a HARQ (Hybrid Automatic Repeat reQuest) in awireless communication system, and more particularly, for an optimizeddownlink HARQ operation when time alignment timer is not running or atan expiry of time alignment timer.

To achieve this and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided a method of processing data for a HARQ (HybridAutomatic Repeat Request) operation in a wireless communication system,the method comprising: receiving a control signaling from a network;receiving a data based on the received control signaling; decoding thereceived data; and generating a positive response message (ACK) if thereceived data is successfully decoded or a negative response message(NACK) if the received data is not successfully decoded, wherein thegenerated positive or negative response message is not transmitted tothe network when a timer is expired or not running.

Also, To achieve this and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, there is also provided a method of processing data for a HARQ(Hybrid Automatic Repeat Request) operation in a wireless communicationsystem, the method comprising: receiving a control signaling from anetwork; receiving a data based on the received control signaling; anddiscarding the received data when a timer is expired or not running.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an exemplary network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as a mobile communicationsystem to which a related art and the present invention are applied;

FIG. 2 shows an exemplary view of related art control plane architectureof a radio interface protocol between a terminal and an E-UTRAN;

FIG. 3 shows an exemplary view of related art user plane architecture ofa radio interface protocol between a terminal and an E-UTRAN;

FIG. 4 is an exemplary view showing a HARQ operation method for aneffective data transmission;

FIG. 5 shows an exemplary view of a contention based random accessprocedure;

FIG. 6 shows an exemplary view of a non-contention based random accessprocedure;

FIG. 7 shows a first exemplary embodiment of downlink HARQ operation ofmobile terminal according to the present invention; and

FIG. 8 shows a second exemplary embodiment of downlink HARQ operation ofmobile terminal according to the present invention.

MODE FOR THE INVENTION

One aspect of this disclosure relates to the recognition by the presentinventors about the problems of the related art as described above, andfurther explained hereafter. Based upon this recognition, the featuresof this disclosure have been developed.

Although this disclosure is shown to be implemented in a mobilecommunication system, such as a UMTS developed under 3GPPspecifications, this disclosure may also be applied to othercommunication systems operating in conformity with different standardsand specifications.

Hereinafter, description of structures and operations of the preferredembodiments according to the present invention will be given withreference to the accompanying drawings.

In general, a terminal (or UE) may perform a random access procedure inthe following cases: 1) when the terminal performs an initial accessbecause there is no RRC Connection with a base station (or eNB), 2) whenthe terminal initially accesses to a target cell in a handoverprocedure, 3) when it is requested by a command of a base station, 4)when there is uplink data transmission in a situation where uplink timesynchronization is not aligned or where a specific radio resource usedfor requesting radio resources is not allocated, and 5) when a recoveryprocedure is performed in case of a radio link failure or a handoverfailure.

In the LTE system, the base station allocates a dedicated random accesspreamble to a specific terminal, and the terminal performs anon-contention random access procedure which performs a random accessprocedure with the random access preamble. In other words, there are twoprocedures in selecting the random access preamble: one is a contentionbased random access procedure in which the terminal randomly selects onewithin a specific group for use, another is a non-contention basedrandom access procedure in which the terminal uses a random accesspreamble allocated only to a specific terminal by the base station. Thedifference between the two random access procedures is that whether ornot a collision problem due to contention occurs, as described later.And, the non-contention based random access procedure may be used, asdescribed above, only in the handover procedure or when it is requestedby the command of the base station.

Based on the above description, FIG. 5 shows an operation procedurebetween a terminal and a base station in a contention based randomaccess procedure.

First, a terminal in the contention based random access randomly mayselect a random access preamble within a group of random accesspreambles indicated through system information or a handover command,may select PRACH resources capable of transmitting the random accesspreamble, and then may transmit the selected random access preamble to abase station (Step 1).

After transmitting the random access preamble, the terminal may attemptto receive a response with respect to its random access preamble withina random access response reception window indicated through the systeminformation or the handover command (Step 2). More specifically, therandom access response information is transmitted in a form of MAC PDU,and the MAC PDU may be transferred on the Physical Downlink SharedChannel (PDSCH). In addition, the Physical Downlink Control Channel(PDCCH) is also transferred such that the terminal appropriatelyreceives information transferred on the PDSCH. That is, the PDCCH mayinclude information about a terminal that should receive the PDSCH,frequency and time information of radio resources of the PDSCH, atransfer format of the PDSCH, and the like. Here, if the PDCCH has beensuccessfully received, the terminal may appropriately receive the randomaccess response transmitted on the PDSCH according to information of thePDCCH. The random access response may include a random access preambleidentifier (ID), an UL Grant, a temporary C-RNTI, a Time AlignmentCommand, and the like. Here, the random access preamble identifier isincluded in the random access response in order to notify terminals towhich information such as the UL Grant, the temporary C-RNTI, and theTime Alignment Command would be valid (available, effective) because onerandom access response may include random access response informationfor one or more terminals. Here, the random access preamble identifiermay be identical to the random access preamble selected by the terminalin Step 1.

If the terminal has received the random access response valid to theterminal itself, the terminal may process each of the informationincluded in the random access response. That is, the terminal appliesthe Time Alignment Command, and stores the temporary C-RNTI. Inaddition, the terminal uses the UL Grant so as to transmit data storedin a buffer of the terminal or newly generated data to the base station(Step 3). Here, a terminal identifier should be essentially included inthe data which is included in the UL Grant (message 3). This is because,in the contention based random access procedure, the base station maynot determine which terminals are performing the random accessprocedure, but later the terminals should be identified for contentionresolution. Here, two different schemes may be provided to include theterminal identifier. A first scheme is to transmit the terminal's cellidentifier through the UL Grant if the terminal has already received avalid cell identifier allocated in a corresponding cell prior to therandom access procedure. Conversely, the second scheme is to transmitthe terminal's unique identifier (e.g., S-TMST or random TD) if theterminal has not received a valid cell identifier prior to the randomaccess procedure. In general, the unique identifier is longer than thecell identifier. In Step 3, if the terminal has transmitted data throughthe UL Grant, the terminal starts the contention resolution timer.

After transmitting the data with its identifier through the UL Grantincluded in the random access response, the terminal waits for anindication (instruction) of the base station for the contentionresolution. That is, the terminal attempts to receive the PDCCH so as toreceive a specific message (Step 4). Here, there are two schemes toreceive the PDCCH. As described above, if the terminal identifiertransmitted via the UL Grant is the cell identifier, the terminalattempts to receive the PDCCH by using its own cell identifier. If theterminal identifier transmitted via the UL Grant is its uniqueidentifier, the terminal attempts to receive the PDCCH by using thetemporary C-RNTI included in the random access response. Thereafter, forthe former, if the PDCCH (message 4) is received through its cellidentifier before the contention resolution timer is expired, theterminal determines that the random access procedure has beensuccessfully (normally) performed, thus to complete the random accessprocedure. For the latter, if the PDCCH is received through thetemporary cell identifier before the contention resolution timer isexpired, the terminal checks data (message 4) transferred by the PDSCHthat the PDCCH indicates. If the unique identifier of the terminal isincluded in the data, the terminal determines that the random accessprocedure has been successfully (normally) performed, thus to completethe random access procedure.

FIG. 6 shows an operation procedure between a terminal and a basestation in a non-contention based random access procedure. As comparedwith the contention based random access procedure, the random accessprocedure is determined to be successfully performed by receiving therandom access response information in the non-contention based randomaccess procedure, thus to complete the random access process.

In general, the non-contention based random access procedure may beperformed in the following two cases: one is the handover procedure, andthe other is a request by the command of the base station. To becertain, the contention based random access procedure may also beperformed in those two cases. First, for the non-contention based randomaccess procedure, it is important to receive, from the base station, adedicated random access preamble without having any possibility ofcontention. Here, a handover command and a PDCCH command may be used toassign the random access preamble. Then, after the random accesspreamble dedicated to only the terminal itself has been assigned fromthe base station, the terminal transmits the preamble to the basestation. Thereafter, the method for receiving the random access responseinformation is the same as that in the above-described contention basedrandom access procedure.

According to a first embodiment of the present invention, if theterminal is not time-aligned with the base station and the terminalreceives data in HARQ process, the present invention proposes to discardthe received data and not to send any HARQ feedback. Namely, asillustrated in FIG. 7, when the terminal (that is not time-aligned withthe base station) receives a PDCCH (Physical Downlink Control Channel)including its own C-RNTI (Cell-Radio Network Temporary Identifier) orSPS (Semi-Persistent Scheduling), the terminal may check whether thereceived PDCCH includes PDSCH radio resource information that theterminal has to be received. If such PDCCH is received by the terminal,the present invention may propose not to attempt to receive the PDSCHradio resource information or not to decode the received data on thePDSCH. Further, the terminal may discard the received data on the PDSCH,and may not send any HARQ feedback (i.e., ACK signal or NACK signal)corresponding to the received data.

According to a second embodiment of the present invention, if theterminal is not time-aligned with the base station and the terminalreceives data in HARQ process, the present invention proposes to decodethe received data but not to send any HARQ feedback. Namely, asillustrated in FIG. 8, when the terminal (that is not time-aligned withthe base station) receives a PDCCH (Physical Downlink Control Channel)including its own C-RNTI (Cell-Radio Network Temporary Identifier) orSPS (Semi-Persistent Scheduling), the terminal may check whether thereceived PDCCH includes PDSCH radio resource information that theterminal has to be received. If such PDCCH is received by the terminal,the present invention may propose to attempt to receive the PDSCH radioresource information and to decode the received data on the PDSCH. Basedon a result of the decoding, the terminal may determine whether to sendan ACK signal or to send a NACK signal. In present invention, althoughsuch determination may be made by the terminal, such ACK or NACK signalshould not be transmitted to the base station. Further, if the receiveddata is successfully decoded and a TAC (Timing Advance Command) isincluded in the received data, the terminal may apply the TAC and maystart a TAT (Time Alignment Timer).

Further, the terminal may discard the received data on the PDSCH, andmay not send any HARQ feedback (i.e., ACK signal or NACK signal)corresponding to the received data. Also, if the received data issuccessfully decoded and the TAC is included in the received data, theterminal may apply the TAC and may start the TAT. In this case, thepresent invention proposes not to transmit an ACK from the terminal tothe base station. In general, after receiving the data in downlink, theterminal may know radio resource(s) (i.e. frequency, time, code, etc) ofHARQ feedback associated with the reception of the data. More in detail,the terminal may extract the radio resource(s) of the HARQ feedback byreceiving a control signal (i.e. PDCCH). Accordingly, the terminal maydecode the received data, may determine a kind of HARQ feedback (e.g.ACK or NACK) based on a result of the decoding, and may transmit theHARQ feedback to the base station. However, the terminal may not be ableto transmit the HARQ feedback to the base station within a transmissiontiming because a processing time to perform all above mentioned stepsmay take too long. Further, there is possibility that some of receivedTAC other that a random access channel procedure may be discarded.

The present invention proposes methods of handling a HARQ soft buffer ofthe terminal when the terminal is not time-aligned with the base stationand the terminal receives a PDCCH including its own a C-RNTI or SPS(Semi-Persistent Scheduling) C-RNTI. Here, the PDCCH includes PDSCHradio resource information that the terminal has to be received.

In a first method, the present invention proposes the terminal to flushdata or contents of all soft buffers (i.e., HARQ soft buffers) after acompletion of the data decoding. Namely, if the terminal (i.e. nottime-aligned terminal with the base station) receives data in a HARQprocess, the received data is stored in a soft buffer. Then the storeddata in the soft buffer is decoded. If the data decoding is successfullyperformed, the received data may be further processed and may bedelivered to an upper layer. However, even if the data decoding issuccessfully performed, a HARQ feedback (i.e. ACK) is not transmitted tothe base station. Here, as the data decoding is completed, the terminalmay flush the stored data in all HARQ soft buffers. If the data decodingis not successfully performed, a HARQ feedback (i.e. NACK) is also nottransmitted to the base station, and the terminal may also flush thestored data in all HARQ soft buffers.

In a second method, the present invention proposes the terminal to flushall data or contents of soft buffers after a completion of the datadecoding and the data decoding is successfully performed. Namely, if theterminal (i.e. not time-aligned terminal with the base station) receivesdata in a HARQ process, the received data is stored in a soft buffer.Then the stored data in the soft buffer is decoded. If the data is notsuccessfully decoded, the terminal may keep the received data in thesoft buffer. Then, the terminal may wait to receive a retransmission ofthe data from the base station. Once the terminal receives theretransmitted data, the terminal may try to combine the retransmitteddata with a currently existed data in the soft buffer. After combining,the terminal may try to decode the combined data again. If the combineddata still can not be decoded, the terminal would wait to receiveanother data retransmission. In contrast, if the data decoding for thecombined data is successfully performed, the terminal may flush the datain the soft buffer at this time.

In a third method, the terminal may replace currently existed data orcontent in the soft buffer with a new data only when the new data istransmitted from the base station. Here, the terminal may not flush thedata in the soft buffer. Namely, the currently existed data is replacedwith the new data only when a NDT of the terminal is toggled. In thiscase, the data in the soft buffer is not flushed even if the TAT isexpired or is not running.

In a forth method, the present invention proposes the terminal to flushdata in the soft buffer all the time. Namely, if the terminal receivesany data in the HARQ process, such data is stored in the soft buffer.However, the data in the soft buffer is flushed immediately.

The present disclosure may provide a method of processing data for aHARQ (Hybrid Automatic Repeat Request) operation in a wirelesscommunication system, the method comprising: receiving a controlsignaling from a network; receiving a data based on the received controlsignaling; decoding the received data; generating a positive responsemessage (ACK) if the received data is successfully decoded or a negativeresponse message (NACK) if the received data is not successfullydecoded; replacing data currently in a soft buffer with the receiveddata after the data is received; flushing the received data in the softbuffer when the positive response message is generated or when the timeris expired or not running; flushing the received data in the soft bufferafter the received data is decoded, wherein the generated positive ornegative response message is not transmitted to the network when a timeris expired or not running, the timer is a Time Alignment timer (TAT),the control signaling is a downlink assignment, the downlink assignmentincludes at least one of downlink scheduling information, a C-RNTI(Cell-Radio Network Temporary Identifier), and a Semi-persistentScheduling C-RNTI, the data is a transport block (TB), and the receiveddata is kept in the soft buffer even when the timer is expired or notrunning.

It can be said that the present invention may also provide a method ofprocessing data for a HARQ (Hybrid Automatic Repeat Request) operationin a wireless communication system, the method comprising: receiving acontrol signaling from a network; receiving a data based on the receivedcontrol signaling; and discarding the received data when a timer isexpired or not running, wherein the timer is a Time Alignment timer(TAT), the control signaling is a downlink assignment, the downlinkassignment includes at least one of downlink scheduling information, aC-RNTI (Cell-Radio Network Temporary Identifier), and a Semi-persistentScheduling C-RNTI, and the data is a transport block (TB).

Although the present disclosure is described in the context of mobilecommunications, the present disclosure may also be used in any wirelesscommunication systems using mobile devices, such as PDAs and laptopcomputers equipped with wireless communication capabilities (i.e.interface). Moreover, the use of certain terms to describe the presentdisclosure is not intended to limit the scope of the present disclosureto a certain type of wireless communication system. The presentdisclosure is also applicable to other wireless communication systemsusing different air interfaces and/or physical layers, for example,TDMA, CDMA, FDMA, WCDMA, OFDM, EV-DO, Wi-Max, Wi-Bro, etc.

The exemplary embodiments may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Field Programmable Gate Array (FPGA), Application SpecificIntegrated Circuit (ASIC), etc.) or a computer readable medium (e.g.,magnetic storage medium (e.g., hard disk drives, floppy disks, tape,etc.), optical storage (CD-ROMs, optical disks, etc.), volatile andnon-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs,SRAMs, firmware, programmable logic, etc.).

Code in the computer readable medium may be accessed and executed by aprocessor. The code in which exemplary embodiments are implemented mayfurther be accessible through a transmission media or from a file serverover a network. In such cases, the article of manufacture in which thecode is implemented may comprise a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Of course, thoseskilled in the art will recognize that many modifications may be made tothis configuration without departing from the scope of the presentdisclosure, and that the article of manufacture may comprise anyinformation bearing medium known in the art.

As the present disclosure may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalents of such metes and bounds are therefore intendedto be embraced by the appended claims.

What is claimed:
 1. A method of performing a HARQ (Hybrid AutomaticRepeat reQuest) operation in a wireless communication system, the methodcomprising: starting a Time Alignment Timer (TAT) when a Timing AdvanceCommand (TAC) is received, wherein the TAC is time alignment informationfor an uplink time alignment; attempting to decode received data in abuffer; generating a positive acknowledgement (ACK) if the received datain the buffer is successfully decoded or a negative acknowledgement(NACK) if the received data in the buffer is not successfully decoded;wherein the generated positive acknowledgment (ACK) or negativeacknowledgment (NACK) is not provided to a physical layer fortransmitting to a network if the Time Alignment Timer (TAT) is expired.2. The method of claim 1, further comprising: replacing data currentlyin the buffer with the received data if a new transmission is indicatedfor the HARQ operation.
 3. The method of claim 1, further comprising:combining the received data with data currently in the buffer if aretransmission is indicated for the HARQ operation.
 4. The method ofclaim 1, further comprising: delivering the decoded data to adisassembly and demultiplexing entity if it is a successful decoding ofthe received data in the buffer.
 5. The method of claim 1, wherein thebuffer is a soft buffer, and the received data is received from thenetwork according to a control signaling.
 6. The method of claim 2,wherein the control signaling includes at least one of downlinkscheduling information, a C-RNTI (Cell-Radio Network TemporaryIdentifier), and a Semi-persistent Scheduling C-RNTI.
 7. A UserEquipment (UE) performing a HARQ (Hybrid Automatic Repeat reQuest)operation in a wireless communication system, the UE comprising: acontroller is configured to: start a Time Alignment Timer (TAT) when aTiming Advance Command (TAC) is received, wherein the TAC is timealignment information for an uplink time alignment; attempt to decodereceived data in a buffer; generate a positive acknowledgement (ACK) ifthe received data in the buffer is successfully decoded or a negativeacknowledgement (NACK) if the received data in the buffer is notsuccessfully decoded; wherein the generated positive acknowledgment(ACK) or negative acknowledgment (NACK) is not provided to a physicallayer for transmitting to a network if the Time Alignment Timer (TAT) isexpired.
 8. The User Equipment (UE) of claim 7, wherein the controlleris further configured to: replace data currently in the buffer with thereceived data if a new transmission is indicated for the HARQ operation.9. The User Equipment (UE) of claim 7, wherein the controller is furtherconfigured to: combine the received data with data currently in thebuffer if a retransmission is indicated for the HARQ operation.
 10. TheUser Equipment (UE) of claim 7, wherein the controller is furtherconfigured to: deliver the decoded data to a disassembly anddemultiplexing entity if it is a successful decoding of the receiveddata in the buffer.
 11. The User Equipment (UE) of claim 7, wherein thebuffer is a soft buffer, and the received data is received from thenetwork according to a control signaling.
 12. The User Equipment (UE) ofclaim 11, wherein the control signaling includes at least one ofdownlink scheduling information, a C-RNTI (Cell-Radio Network TemporaryIdentifier), and a Semi-persistent Scheduling C-RNTI.